The crossing, which is the largest for passenger and goods transit, was already evacuated before the shelling.

Residents in nearby towns also fled the area prior to the fighting.

The continuing turmoil has been raising serious concerns that regional powers - Shi'ite-inclined Iran, and the world's top oil exporter Saudi Arabia along with other Sunni Muslim states in the region - are throwing their weight behind the Houthi and the effectively-exiled Yemeni president Abd-Rabbu Mansour Hadi respectively.